1. Field of the Invention
The present invention relates to a solid-state imaging device configured by mounting an imaging element such as a CCD on a base and a method for producing the same.
2. Related Background Art
Solid-state imaging devices are used widely for video cameras and still cameras, and are provided in a form of a package in which an imaging element such as a CCD is mounted on a base made of an insulating material and a light-receptive region is covered with a transparent plate. In order to miniaturize the device, the imaging element is mounted on the base while keeping a bare chip state (for example, see JP 2000-58805 A). Such a conventional example of the solid-state imaging devices will be described below with reference to FIG. 7.
A base 31 in FIG. 7 is made of ceramic or a plastic resin and has a frame form in planar shape having an aperture 32 in its center portion. A bottom face of the base 31 is recessed at a region along a periphery of the aperture 32 so as to form a recess 33. The bottom face of the base 31 is provided with a wiring 34 made of a gold plate layer, which extends from the vicinity of the aperture 32 to a peripheral end face of the base 31. On the face of the recess 33 with the wiring 34 formed thereon, an imaging element 35 configured with a CCD and the like is mounted, which is connected with the wiring 34. The imaging element 35 is disposed so that its light-receptive region 35a faces the aperture 32. On a top face of the base 31, a transparent plate 36 made of glass is attached so as to cover the aperture 32. The surroundings of an end portion of the imaging element 35 are filled with a sealing resin 37 so as to hermetically seal a gap between the end portion of the imaging element 35 and the base 31. In this way, the light-receptive region 35a is disposed within a closed space formed with the aperture 32.
On the same surface of the imaging element 35 as the light-receptive region 35a, an electrode pad (not illustrated) connected with a circuit for the light-receptive region 35a is disposed, and a bump (protrusion electrode) 38 is provided on the electrode pad. An end portion of the wiring 34 adjacent to the aperture 32 forms an internal terminal portion, which is connected with the electrode pad for the imaging element 35 via the bump 38.
This solid-state imaging device is to be mounted on a circuit board, in a position as shown in the drawing, with a transparent plate 36 side facing upward. A portion of the wiring 34 that is disposed on the bottom face of the outer peripheral area (the area outside the recess 33) of the base 31 forms an external terminal portion, which is used for the connection with an electrode on the circuit board. A lens barrel (not illustrated) with an imaging optical system incorporated therein is provided above the transparent plate 36, where a relative positional relationship with the photo-receptive region 35a is set with predetermined accuracy. By means of the imaging optical system incorporated in the lens barrel, light from an object to be imaged is collected onto the light-receptive region 35a so as to effect photoelectric conversion.
In addition, as well as the structure of the base 31 in the configuration shown in FIG. 7, there is a known example of a solid-state imaging device employing a base having a flat planar shape as the whole without the recess 33 on the face for mounting the imaging element 35 (for example, see JP 2002-43554 A). In such a case, an external terminal portion disposed at a peripheral end portion of a base is connected with an electrode on a circuit board by means of a solder ball and the like having a large diameter. The solder ball functions so as to adjust an interval between the bottom face of the imaging element 35 and a face of the circuit board as well.
According to the configuration of the above-described conventional solid-state imaging devices, however, it is difficult to obtain a sufficient flatness of the base 31. That is to say, since the base 31 has a frame form having the aperture 32, there is a tendency to generate a curl and a warp in its cross-sectional shape. When the flatness of the face of the recess 33 to which the imaging element 35 is to be mounted is not sufficient, then the position of the imaging element 35 becomes unstable, resulting in the lens barrel not being aligned accurately with respect to the light-receptive region 35a. 
Furthermore, in the conventional examples, the wiring is formed by plating. In this respect, a process for applying the plating to the base 31 is complicated, and the process tends to generate a variation in dimensional accuracy of the formed wiring 34 and requires high cost.